1. Field of the Invention
The present invention relates to a flow sensor, which is capable of measuring a flow rate of a fluid, and more specifically, relates to a flow passage structure for such a flow sensor.
2. Description of the Related Art
Heretofore, for example, for measuring the flow rate of a fluid such as air or the like, a flow sensor having a fluid passage through which the fluid flows, and a sensor disposed facing the fluid passage, has been known. Such a flow sensor, for example as disclosed in Japanese Laid-Open Patent Publication No. 2003-149017, is formed with a fluid passage inside of a main block through which the fluid flows. The main block is equipped with an upstream side sensor flow passage connected to an upstream side of the fluid passage, and a downstream side sensor flow passage connected to a downstream side of the fluid passage. In addition, a sensor conduit mutually interconnects the upstream side sensor flow passage and the downstream side sensor flow passage, with a sensor element being disposed in the sensor conduit.
However, in the aforementioned conventional technique, there is a fear that moisture or the like contained within the fluid may traverse the inner wall surfaces of the fluid passages and intrude into the upstream side sensor flow passage, the sensor conduit, and the downstream side sensor flow passage. Consequently, malfunctioning of the sensor element arranged facing the sensor conduit may occur, caused by intruding moisture or the like, such that the flow rate of the fluid cannot be measured reliably by the sensor element.